Color-matched digital playback

ABSTRACT

Perceptually correctly rendering a color-matched image of a digital imagery including receiving and storing a digital data set representing the digital imagery; computing a three-dimensional lookup table (3-D LUT) using a color transform stack; simulating a real-time film-appearance using the computed 3-D LUT mapped on a graphics card; projecting a first image generated by the graphics card; comparing the first image with a second image generated by a film negative of the digital imagery; and repeating the computing, the simulating, the projecting, and the comparing when the first image is not perceptually substantially similar to the second image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of co-pending U.S.Provisional Patent Application Ser. No. 60/528,051, entitled“Color-Matched Digital Playback”, filed Dec. 9, 2003. Benefit ofpriority of the filing date of Dec. 9, 2003 is hereby claimed, and thedisclosure of the Provisional Patent Application is hereby incorporatedby reference.

BACKGROUND

Digital images are typically created, viewed, and manipulated usingcomputers. Thus, judgments concerning the desired appearance of thedigital images are made based on how the images appear when displayed ondigital display devices. When the digital images are created andmanipulated for a motion picture, the image data stored on the computermust be converted into film images for projection in a theater.

Digital film recorders are used to convert the digital images intoimages on photosensitive motion picture film. The conventional digitalfilm recorders use a light source (e.g., a laser) to expose each frameof the film as necessary to produce the desired image in the frame. Thefilm is then advanced to the next frame and the process is repeated.When a strip of film has been recorded, it is sent to a laboratory fordevelopment into a color negative and, later, a positive print.

To provide a high quality digital motion picture, it is desirable tohave the appearance of the motion picture that is projected and viewedby a theater audience match the appearance contemplated by the producer.Thus, the color of each location on the exposed film shouldsubstantially match the color of the corresponding picture element(“pixel”) on the digital display device used by the producer to producethe image. That is, color accurate renditions of the digital filmimagery are desired. Matching the calorimetric appearance of a digitalfilm, however, is an intricate problem because the appearance isinfluenced by the film development processes, disparate projectiontechnologies, and varying viewing environments.

Conventional approaches to producing color images on film that match theoriginally produced digital images include using a measurement-basedsolution. By characterizing the digital display device and filmresponse, a visual correspondence can be computed between the film andthe digital projection. However, simply relying on the photometrically“correct” solution does not typically yield satisfactory results becausethe solution ignores the perceptual impact of differing viewingenvironments.

One difficulty in producing a film image that corresponds visually tothe original digital image produced and/or stored on a computer includeswhat is sometimes referred to as a “gamut mismatch”, which involves theinability of the film to reproduce all the colors reproducible on thedigital display device. One conventional solution is to map the colors,which are outside the film's gamut, to the closest point on the surfaceof the film's gamut while maintaining the colors that are initiallyinside the gamut. This solution, however, results in abrupt colorchanges and produces banding artifacts in the final image.

SUMMARY

The present invention provides method and apparatus for perceptuallycorrectly rendering a color-matched image of a digital imagery. In oneimplementation, the method comprises: receiving and storing a digitaldata set representing the digital imagery; computing a three-dimensionallookup table (3-D LUT) using a color transform stack; simulating areal-time film-appearance using the computed 3-D LUT mapped on agraphics card; projecting a first image generated by the graphics card;comparing the first image with a second image generated by a filmnegative of the digital imagery; and repeating the computing, thesimulating, the projecting, and the comparing when the first image isnot perceptually substantially similar to the second image.

In another implementation, a color-matched digital image renderercomprises: a disk array for storing a digital data set represented bythe digital imagery; a three-dimensional lookup table (3-D LUT) forsimulating a real-time film-appearance of the digital data set; amapping element for mapping the 3-D LUT on a trilinear interpolator of agraphics card; a projector for displaying a first image generated by thegraphics card, such that the first image can be compared with a secondimage generated by a film negative of the digital imagery, wherein a new3-D LUT is generated when the first image is not perceptuallysubstantially similar to the second image.

In another implementation, a computer program, stored in a tangiblestorage medium, for rendering a color-matched image of a digitalimagery, the program comprising executable instructions that cause acomputer to: receive and store a digital data set represented by thedigital imagery; compute a three-dimensional lookup table (3-D LUT)using a color transform stack; simulate a real-time film-appearanceusing the computed 3-D LUT mapped on a graphics card; project a firstimage generated by the graphics card; compare the first image with asecond image generated by a film negative of the digital imagery; andrepeat the computing, the simulating, the projecting, and the comparingwhen the first image is not perceptually substantially similar to thesecond image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one example of a color management system, whichincludes three pipelines.

FIG. 2 illustrates one example of a user interface loop for producing a3-D LUT.

FIGS. 3A and 3B illustrate one example of constructing a 3-D LUT in aprocess referred to as a “domain of influence” process, in which therelative influence of each color matrix is represented over each range.

FIG. 4 illustrates one example of a 3-D LUT processing using trilinearinterpolation hardware.

FIG. 5 illustrates one example of a color management method for enablinga color-matched digital image rendering.

DETAILED DESCRIPTION

To address some of the difficulties facing the conventional approachesto producing color images in motion pictures, various implementations ofthe present invention are configured to provide methods and systems forcolor-matched digital image rendering that accurately simulates colorresponse of the film. The implementations enable the artist to use thehighly accurate color judgment ability to view, compare, and produce a“perceptually-correct” match between the digitally-projected image andthe film image projection using a three dimensional lookup table totransform color.

Several illustrative examples of implementations are presented below.These examples are not exhaustive and additional examples and variationsare also described later.

FIG. 1 illustrates one example of a color management system 100, whichincludes three pipelines 110, 120, 130. The pipelines 120 and 130receive an originally produced digital imagery 102.

The pipeline 120 is a digital-image-rendering pipeline that receives thedigital imagery 102 and stores the imagery in a disk array 122. In oneimplementation, the received digital data is arranged in the disk array122 to allow an efficient projection by the digital projector 126.

In the illustrated implementation of FIG. 1, the stored digital data inthe disk array 122 is transformed by a trilinear interpolator 124 for areal-time “film-appearance” simulation, which is implemented in hardwareby applying a three-dimensional lookup table (3-D LUT). The 3-D LUT is atable-organized data set defined as three-dimensional input vectors thatare mapped independently to three-dimensional output vectors. In oneimplementation, (32×32×32) unique entries are maintained, withintermediate samples evaluated using hardware-accelerated trilinearinterpolation.

The conventional digital-image rendering pipeline does not use the 3-DLUT in simulating the film gamut because applying and interpolatinglarge three-dimensional data sets in a CPU is computationally expensive.FIG. 1, however, implements the realization that interpolating thethree-dimensional data set in the 3-D LUT uses a substantially similarmathematical technique as the trilinear texture interpolation that iscommonly used to evaluate MIP-mapped textures on conventional graphicscards. By efficiently mapping the 3-D LUT sampling technique onto thegraphics card, the real-time full color “film-appearance” simulation canbe realized in hardware.

Since the 3-D LUT lookup operation is already supported in silicon onexisting graphics hardware, the LUT is loaded on the graphics card as a3-D (or volumetric) texture to apply the lookup table. As the image isdrawn, each incoming pixel value is treated as an index, and is accessedin the 3-D data set. The resulting value, which defines the final colorto draw, is sent to the display. Thus, a “dependent texture” read isused in the RGB domain to adjust the pixel colors as the colors aredrawn to the frame buffer.

Once the digital data is transformed by the real-time “film-appearance”simulation 124, the transformed digital data is then transmitted to adigital projector 126 for display. In one implementation, the digitalprojector 126 includes a digital light processing (DLP) projector thatuses an optical semiconductor to digitally manipulate light. In anotherimplementation, the digital projector 126 includes a liquid crystaldisplay (LCD) device.

The pipeline 130 is a traditional film pipeline that receives thedigital imagery 102 and records the imagery on a color negative 132using a laser film recorder 130. The negative 132 is developed into apositive print 134 and is projected onto a film projector 136.

The pipeline 110 is a user interface loop for a producer (or an artist)of the digital image with access to the standard palette of colorcorrection tools 114 including tools for color balance, hue/saturation,and gamma adjustments. A complex color transform is iteratively built upby superimposing multiple adjustment layers on user-defined subsets ofthe color gamut. A number of transformation layers are used to “bake” orproduce a single 3-D LUT.

Another reason the conventional digital-image-rendering pipeline doesnot use the 3-D LUT in simulating the film gamut is the lack of aneffective solution for computing the three-dimensional data sets neededto appropriately transform the images. The conventional approach uses ameasurement-based solution that takes a set of samples characterizingthe response of film and the display device, and uses a simulation ofthe human visual system to predict the mapping for all colors. However,since current simulations of the human visual system do not have theaccuracy that the film industry requires, the conventional approachcannot provide a satisfactory solution. Furthermore, this approachrelies on the flawed assumption of what constitutes the “correct”transform. An ideal image is not one that produces the “mathematicallycorrect” response, but one that is deemed by the artist to be“perceptually correct”. For example, in the traditional numericalsimulation approach, the final transform is rigidly defined and cannotbe adjusted to an end user bias. If an artist views the color simulationand requests the model to be “tweaked”, such as “make the midtoneswarmer”, it is very difficult to use traditional 3-D LUT interactionmodels to achieve the desired results.

In one implementation of the present invention, the artist uses thehighly accurate color judgment ability to view, compare, and produce a“perceptually-correct” match 104 between the digital projection 126produced in the digital-image-rendering pipeline 120 and the test filmprojection 136 produced in the traditional film pipeline 130. Theproduction of the “perceptually-correct” match 104 includes a feedbackto the user interface loop 110 to allow the artist to interactivelymanipulate the 3-D LUT color transform 112 until a substantial match ofthe renditions of the digital projection 126 and the test filmprojection 136 is achieved.

Thus, producing a “perceptually-correct” solution 104, which includesthe effects of differing display gamuts and viewing environments, isreduced to a simple exercise in color grading. The resulting colortransformation is “baked” into the 3-D LUT 112, which is then applied inreal-time during the “film-appearance” simulation 124 of thedigital-image-rendering pipeline 120. The 3-D LUT is used toindependently map every input color to a display-specific output color.

FIG. 2 illustrates one example of a user interface loop 110 forproducing the 3-D LUT 112. The user interface loop 110 includes a colorcorrection stack 200 and visualization options 206.

Slots in the color-correction stack 200 are used such that the resultsof each processing element in a particular slot are fed to the nextlevel up. Thus, the processing element in each slot performs a simpleadjustment, such as an adjustment to color balance, matrix, hue,saturation, or gamma correction. For each image operation, the user candefine a “partition” 202 of the color space for which to apply thetransform. The partition 202 is typically specified as limits to thehue, saturation, and value of incoming lattice point, and includes auser-specified mask. However, in order to minimize discontinuities inthe final table, partitions 204 can be “soft” edges, where the colorcorrections are only partially applied near the selection boundaries.

In the illustrated example of FIG. 2, four image visualization optionsor modes 206 are allowed to aid the artist in producing the color (film)transformation. The options include: final image simulation; selectionpartition composited over a desaturated image; selection partitioncomposited over a constant color; and a matte image (i.e., grayscale).

The final image simulation mode shows the results of the complete colorcorrection stack. The selection partition composited over a desaturatedimage mode shows the currently-edited layer in full color, which iscomposited over a desaturated version of all layers underneath. This isuseful in adjusting the hue-based selection partitions. The selectionpartition composited over a constant color mode shows thecurrently-edited layer in full color, which is composited over aconstant color (i.e., either black or white). This is useful inadjusting the value-based selection partitions. The matte image modeshows in grayscale the current layer's selection matte.

FIGS. 3A and 3B illustrate one example of constructing a 3-D LUT in aprocess 300 referred to as a “domain of influence” process, in which therelative influence of each color matrix is represented over each range.For example, the user might choose to specify a different colortransformation in the shadows, midtones, and highlights of the image.Thus, in the illustrated example, M1 represents the shadow, M2represents the midtone, and M3 represents the highlight.

Initially, an input identity RGB transform is computed. Then, for eachcolor transformation on the color stack, the input RGB transform isconverted based on the input RGB value weighted by the “influence” ofthat color transform. Boundaries 302, 304 of the influence of each colormatrix are interpolated to produce one lattice point (i.e., one of thedimensions of the three dimensional data) in the 3-D LUT.

FIG. 4 illustrates one example of a 3-D LUT processing 400 usingtrilinear interpolation hardware. In the illustrated example, the LUTprocessing is performed to linearly map the incoming color with the LUTindex. However, in applying the LUT with this method, the input colorsneed to be offset and scaled to preserve the contrast of the image, andaccount for the trilinear interpolation being mathematically ill-definedat the edges of the data set.

In the illustrated example of FIG. 4, the offset and the scale areapplied to the LUT indices as follows:

${Scale} = {{\frac{{LutSize} - 1}{LutSize}.{Offset}} = {\frac{1}{2*{LutSize}}.}}$

Thus, for a (32×32×32) LUT, during the dependent texture read, thelookup indices are defined as:

$\begin{matrix}{{LookupIndex} = {{{Scale}*{InputColor}} + {Offset}}} \\{= {{\left( \frac{31}{32} \right)*{InputColor}} + \left( \frac{1}{64} \right)}}\end{matrix}$

FIG. 5 illustrates one example of a color management process to enable acolor-matched digital image rendering. In the illustrated example, adigital imagery is received at 500. The digital data set represented bythe digital imagery is stored in a disk array at 502. A 3-D LUT iscomputed, at 504, using a color transform stack computed in the userinterface loop of FIG. 1. The 3-D LUT can be computed according to theprocess described in connection with FIG. 1 through FIG. 4.

A real-time film-appearance simulation is performed by mapping thestored digital data set into a three dimensional data set on ahardware-accelerated trilinear interpolator of a graphics card using thecomputed 3-D LUT, at 506. An image generated by the graphics card isthen projected, at 508.

The received digital imagery is also used to generate a film negative at522. A positive print is generated at 524. An image generated by thepositive print is then projected, at 526.

A perceptual match between the image generated by the graphics card andthe image generated by the positive print is performed, at 510, anddetermined, at 512, whether the images are perceptually substantiallysimilar. If the images are not perceptually substantially similar,another 3-D LUT is computed, at 504. Otherwise, if the images areperceptually substantially similar, the color management process isterminated.

In an alternative implementation, a directed graph (DAG) view can beused, instead of the color correction stack, for more complex imageoperation chains. This would allow for arbitrary color correctiondependencies, and would appear to the user to be a standard compositingnode-graph. In another alternative implementation, the 3-D LUT can bedouble buffered to allow for lengthy LUT calculations.

Various implementations of the invention are realized in electronichardware, computer software, or combinations of these technologies. Mostimplementations include one or more computer programs executed by aprogrammable computer. For example, in one implementation, a colormanagement system includes one or more computers executing softwareimplementing the management of colors discussed above. In general, eachcomputer includes one or more processors, one or more data-storagecomponents (e.g., volatile or non-volatile memory modules and persistentoptical and magnetic storage devices, such as hard and floppy diskdrives, CD-ROM drives, and magnetic tape drives), one or more inputdevices (e.g., mice and keyboards), and one or more output devices(e.g., display consoles and printers).

The computer programs include executable code that is usually stored ina persistent storage medium and then copied into memory at run-time. Theprocessor executes the code by retrieving program instructions frommemory in a prescribed order. When executing the program code, thecomputer receives data from the input and/or storage devices, performsoperations on the data, and then delivers the resulting data to theoutput and/or storage devices.

Although various illustrative implementations of the present inventionhave been described, one of ordinary skill in the art will see thatadditional implementations are also possible and within the scope of thepresent invention. For example, although the above-discussedimplementations have been limited to simulating the color effects offilm, these implementations can be used to achieve artistic colormodifications in real-time and in an intuitive manner.

Further, these implementations can also be used in any consumer displaydevice that has “knobs” (e.g., gamma, bias, color matrix, and ared-green-blue/cyan-magenta-yellow (RGB/CMY) interpolator) to adjustpicture characteristics such as hue, saturation, contrast, brightness,and other related characteristics. Thus, when the user adjusts any ofthese outward-facing “interfaces”, a recalculation of the singleinternal 3-D LUT that simulates the desired effect can be performed.

The advantage of these implementations is that any number of arbitrarilycomplex “knobs” can be added without placing additional hardwarerequirements. For example, a “film-look” knob on a television thatsimulates the complex calorimetric appearance of different film stockscan be implemented with the above-discussed implementations. Thesecomplex “knobs” can also be added to acquisition devices such as videocamcorders.

Accordingly, the present invention is not limited to only thoseimplementations described above.

1. A method of rendering a color-matched image of a digital imagery,comprising: receiving and storing a digital data set representing thedigital imagery; computing a three-dimensional lookup table (3-D LUT)using a color transform stack; simulating a real-time film-appearanceusing the computed 3-D LUT mapped on a graphics card; projecting a firstimage generated by the graphics card; comparing the first image with asecond image generated by a film negative of the digital imagery; andrepeating said computing, said simulating, said projecting, and saidcomparing when the first image is not perceptually substantially similarto the second image.
 2. The method of claim 1, wherein said storing adigital data set includes arranging the digital data set in a disk arrayto allow an efficient projection of the first image.
 3. The method ofclaim 1, wherein said simulating a real-time film-appearance includesmapping the digital data set into a three dimensional data set.
 4. Themethod of claim 3, wherein said simulating a real-time film-appearancefurther includes mapping the digital data set on a trilinearinterpolator of the graphics card.
 5. The method of claim 4, whereinsaid simulating a real-time film-appearance further includes loading thethree dimensional data set on the graphics card as a volumetric texture.6. The method of claim 1, wherein said computing a 3-D LUT using a colortransform stack includes performing an adjustment to a color gamut. 7.The method of claim 6, wherein the color gamut includes a color balance.8. The method of claim 6, wherein the color gamut includes a colormatrix.
 9. The method of claim 6, wherein the color gamut includes hue.10. The method of claim 6, wherein the color gamut includes a colorsaturation.
 11. The method of claim 6, wherein the color gamut includesa gamma correction.
 12. The method of claim 6, wherein said performingan adjustment to a color gamut includes partially applying theadjustment near selection boundaries of the digital data set to minimizediscontinuities in the 3-D LUT.
 13. The method of claim 6, wherein saidsimulating a real-time film-appearance further includes providing afinal image simulation to show results of the adjustment to the colorgamut.
 14. The method of claim 6, wherein said simulating a real-timefilm-appearance further includes providing a selection partitioncomposited over a desaturated image to show results of acurrently-edited layer in full color composited over a desaturatedversion of all layers underneath.
 15. The method of claim 6, whereinsaid simulating a real-time film-appearance further includes providing aselection partition composited over a constant color to show results ofa currently-edited layer in full color composited over a constant color.16. The method of claim 6, wherein said simulating a real-timefilm-appearance further includes showing a selection matte of a currentlayer in grayscale.
 17. A color-matched digital image renderer forperceptually correctly rendering a digital imagery, comprising: a diskarray for storing a digital data set represented by the digital imagery;a three-dimensional lookup table (3-D LUT) for simulating a real-timefilm-appearance of the digital data set; a mapping element for mappingthe 3-D LUT on a trilinear interpolator of a graphics card; a projectorfor displaying a first image generated by the graphics card, such thatthe first image can be compared with a second image generated by a filmnegative of the digital imagery, wherein a new 3-D LUT is generated whenthe first image is not perceptually substantially similar to the secondimage.
 18. The renderer of claim 17, wherein the 3-D LUT is configuredusing a color transform stack to adjust a color gamut of the firstimage.
 19. The renderer of claim 18, further comprising a final imagesimulator to show results of the adjustment to the color gamut.
 20. Therenderer of claim 18, further comprising a selection partitioncomposited over a desaturated image to show results of acurrently-edited layer in full color composited over a desaturatedversion of all layers underneath.
 21. The renderer of claim 18, furthercomprising a selection partition composited over a constant color toshow results of a currently-edited layer in full color composited over aconstant color such as black or white.
 22. The renderer of claim 18,further comprising a selection matte of a current layer in grayscale.23. A computer program, stored in a computer readable medium, forrendering a color-matched image of a digital imagery, the programcomprising executable instructions that cause a computer to: receive andstore a digital data set represented by the digital imagery; compute athree-dimensional lookup table (3-D LUT) using a color transform stack;simulate a real-time film-appearance using the computed 3-D LUT mappedon a graphics card; project a first image generated by the graphicscard; compare the first image with a second image generated by a filmnegative of the digital imagery; and repeat said computing, saidsimulating, said projecting, and said comparing when the first image isnot perceptually substantially similar to the second image.
 24. Thecomputer program of claim 23, wherein executable instructions that causea computer to store a digital data set include executable instructionsthat cause a computer to arrange the digital data set in a disk array toallow an efficient projection of the first image.
 25. The computerprogram of claim 23, wherein executable instructions that cause acomputer to simulate a real-time film-appearance include executableinstructions that cause a computer to map the digital data set into athree dimensional data set.
 26. The computer program of claim 25,wherein executable instructions that cause a computer to simulate areal-time film-appearance further include executable instructions thatcause a computer to map the digital data set on a trilinear interpolatorof a graphics card.
 27. The computer program of claim 26, whereinexecutable instructions that cause a computer to simulate a real-timefilm-appearance further include executable instructions that cause acomputer to load the three dimensional data set on the graphics card asa volumetric texture.
 28. The computer program of claim 23, whereinexecutable instructions that cause a computer to compute a 3-D LUT usinga color transform stack include executable instructions that cause acomputer to perform an adjustment to a color gamut.
 29. The computerprogram of claim 28, wherein executable instructions that cause acomputer to perform an adjustment to a color gamut include executableinstructions that cause a computer to partially apply the adjustmentnear selection boundaries to minimize discontinuities in the 3-D LUT.30. The computer program of claim 28, wherein executable instructionsthat cause a computer to simulate a real-time film-appearance furtherinclude executable instructions that cause a computer to provide a finalimage simulation to show results of the adjustment to the color gamut.31. The computer program of claim 28, wherein executable instructionsthat cause a computer to simulate a real-time film-appearance furtherinclude executable instructions that cause a computer to provide aselection partition composited over a desaturated image to show resultsof a currently-edited layer in full color composited over a desaturatedversion of all layers underneath.
 32. The computer program of claim 28,wherein executable instructions that cause a computer to simulate areal-time film-appearance further include executable instructions thatcause a computer to provide a selection partition composited over aconstant color to show results of a currently-edited layer in full colorcomposited over a constant color such as black or white.
 33. Thecomputer program of claim 28, wherein executable instructions that causea computer to simulate a real-time film-appearance further includeexecutable instructions that cause a computer to show a selection matteof a current layer in grayscale.
 34. A renderer for rendering acolor-matched image of a digital imagery, comprising: means forreceiving and storing a digital data set represented by the digitalimagery; means for computing a three-dimensional lookup table (3-D LUT)using a color transform stack; means for simulating a real-timefilm-appearance using the computed 3-D LUT mapped on a graphics card;means for projecting a first image generated by the graphics card; andmeans for comparing the first image with a second image generated by afilm negative of the digital imagery, wherein if the first image is notperceptually substantially similar to the second image, a new 3-D LUT iscomputed by said means for computing and a new first image is generatedand compared to the second image by said means for comparing.
 35. Therenderer of claim 34, wherein said means for storing a digital data setincludes means for operatively arranging the digital data set in a diskarray to allow an efficient projection of the first image.
 36. Therenderer of claim 34, wherein said means for simulating a real-timefilm-appearance includes means for mapping the digital data set into athree dimensional data set.
 37. The renderer of claim 36, wherein saidmeans for simulating a real-time film-appearance further includes meansfor mapping the digital data set on a trilinear interpolator of agraphics card.
 38. The renderer of claim 37, wherein said means forsimulating a real-time film-appearance further includes means forloading the three dimensional data set on the graphics card as avolumetric texture.
 39. The renderer of claim 34, wherein said means forcomputing a 3-D LUT using a color transform stack includes means forperforming an adjustment to a color gamut.
 40. The renderer of claim 39,wherein said means for performing an adjustment to a color gamutincludes means for partially applying the adjustment near selectionboundaries to minimize discontinuities in the 3-D LUT.
 41. The rendererof claim 39, wherein said means for simulating a real-timefilm-appearance further includes means for providing a final imagesimulation to show results of the adjustment to the color gamut.
 42. Therenderer of claim 39, wherein said means for simulating a real-timefilm-appearance further includes means for providing a selectionpartition composited over a desaturated image to show results of acurrently-edited layer in full color composited over a desaturatedversion of all layers underneath.
 43. The renderer of claim 39, whereinsaid means for simulating a real-time film-appearance further includesmeans for providing a selection partition composited over a constantcolor to show results of a currently-edited layer in full colorcomposited over a constant color such as black or white.
 44. Therenderer of claim 39, wherein said means for simulating a real-timefilm-appearance further includes means for showing a selection matte ofa current layer in grayscale.